(1) Field of the Invention
This invention relates to talc dispersions, and concerns more particularly stable aqueous dispersions of talc, having a high solids content, suitable for use in the coating of paper in place of the currently-employed china clay dispersions.
(2) Description of Prior Art
It is well-known in a number of fields to prepare and use high solids aqueous dispersions of clays and clay-like materials. Typically, for example, china clay (Kaolin) has been prepared as a high solids aqueous dispersion for addition to various water-dispersed natural or synthetic resins (latices) subsequently used to coat paper so as to give a surface having the desired properties. White clays such as china clay are, however, rather expensive, and efforts have been made to use talc (a complex hydrated magnesium silicate), a material which should in theory lead to results as good if not better than those achieved using china clay. Unfortunately, talc, unlike china clay, is relatively hydrophobic, and attempts to prepare aqueous talc dispersions, particularly stable high solids aqueous talc dispersions (which are desirable to reduce transport costs and cut drying time), have not been entirely successful. These past attempts to prepare talc dispersions have generally involved selecting particular grades of talc and/or selecting particular dispersing agents (or mixtures thereof) which can be used either to pretreat the talc or simply as part of the dispersion. However, it has not up to now been possible to prepare an aqueous talc dispersion which contains much better than 60 wt % talc and yet which is stable (so that the talc remains properly dispersed), has a viscosity enabling it to be pumped relatively easily, and employs dispersing agents all of which are compatible with the resins with which the talc dispersion is to be used.